Oxidation of benzyl alcohol aiming at a greener reaction

A highly efficient heterogeneous catalyst Ru-Mn-Fe-Cu-O successfully oxidized benzyl alcohol to benzaldehyde in the presence of oxygen using toluene or water as solvent, and without solvent aiming at greener chemistry. This revised version was published online in June 2006 with corrections to the Cover Date.     

One- versus two-electron reaction pathways in the electrocatalytic reduction of benzyl bromide at silver cathodes

The electrocatalytic reduction of benzyl bromide at a silver cathode has been investigated in acetonitrile in the absence and presence of acids, using cyclic voltammetry (CV) and controlled-potential electrolysis (CPE). CV gives rise to two reduction waves, which represent the dissociative 1e⁻ reduction of PhCH₂Br to and Br⁻ followed by a further reduction of the benzyl radical to at more negative potentials. The charge stoichiometry (1e⁻ vs 2e⁻/molecule) and product distribution depend on the applied potential and reaction medium. In the absence of added acids, the reduction of PhCH₂Br at potentials of the first wave is a 1e⁻ process mainly yielding bibenzyl, whereas toluene becomes the principal product at potentials beyond the second wave. The addition of acids strongly modifies the dependence of selectivity on the applied potential. The presence of a strong acid changes the mechanism of the process, which now becomes a 2e⁻ reduction to toluene, even at potentials corresponding to the first reduction wave.     

Formation of N-benzylbenzamide from benzyl phenyl ketone oxime in a system C2H2-KOH-DMSO. Key role of acetylene

Russian Journal of Organic Chemistry -     

Polycondensation of benzyl chloride and its derivatives: A study of the reaction at different temperatures

The polycondensation reactions of benzyl chloride, α-chloroethylbenzene, and benzhydryl chloride in the presence of SnCl₄ or AlCl₃ as catalysts have been investigated in the temperature range between +80° and ?135°C. Polycondensations of benzyl chloride and α-chloroethylbenzene are quite similar in the reaction kinetics and are thought to occur by the same displacement mechanism. Polycondensation of benzhydryl chloride, however, seems to involve the formation of benzhydryl carbonium ions. At low temperatures linear polymers tend to be formed, in contrast with branched polymers produced at room temperature. Steric effects are found to play a major role in protecting polymers from branching at lower temperatures. Polybenzyl polymers are found to be less linear than poly(-α-methylbenzyl), even when prepared at ?135°C.     

A convenient synthesis of the beraprost intermediate: a useful method for introducing a C3 unit at the benzyl position

[reaction: see text] The Heck reaction is a more efficient and reliable method than previous ones for introducing a C3 unit at the benzyl position for the synthesis of Beraprost. Especially, trialkylated long-chain amines such as (n-C(8)H(17))(3)N and (n-C(12)H(25))(3)N resulted in good yields. This development will be used for the industrial synthesis of Beraprost.     

Solvent effects in the reaction between piperazine and benzyl bromide

The reaction between piperazine and benzyl bromide was studied conductometrically and the second order rate constants were computed. These rate constants determined in 12 different protic and aprotic solvents indicate that the rate of the reaction is influenced by electrophilicity (E), hydrogen bond donor ability (α) and dipolarity/polarizability (π*) of the solvent. The LSER derived from the statistical analysis indicates that the transition state is more solvated than the reactants due to hydrogen bond donation and polarizability of the solvent while the reactant is more solvated than the transition state due to electrophilicity of the solvent. Study of the reaction in methanol, dimethyl formamide mixtures suggests that the rate is maximum when dipolar interactions between the two solvents are maximum.     

Mechanistic study on DNA mutation of the cytosine methylation reaction at C5 position

DNA methylation is a crucial epigenetic mark connected to conventionally changing the DNA bases, typically by adding methyl groups into DNA bases. Methylation of cytosine at the C5 position (5-methylcytosine) occurs mostly in the context of cytosine-phosphate-guanine dinucleotides, the methylation of which has important impacts on gene regulation and expression. However, the mechanistic details of this reaction are still debatable concerning the concertedness of the key reaction steps and the roles played by the base that abstracts the proton in the β-elimination and water molecules at the active site. To gain a deeper insight into the formation of 5-mehtylcytosine, an extensive density functional theory (DFT) study was performed with the B3LYP functional in conjunction with different basis sets. Our study has clearly established the mechanistic details of this methylation approach, based on which the roles of conserved active site residues, such as glutamic acid and waters, are well understood. Our results show that the reaction of 5-methylcytosine follows a concerted mechanism in which water molecules are critically involved. Moreover, arginine and alanine give more significant catalytic effects than glutamic acid on the 5-methylcytosine process. Considering the effect of Alanine, Arginine, and one water bridging molecule, the activation energy is 31 kJ mol^?1 calculated at B3LYP/6-31G(d) level of theory.     

A novel stereoselective carbon-chain extension reaction at the C-6 position of 1,6-anhydropyranose

6-Bromo-1,6-anhydro-d-mannose triacetate reacted with a variety of carbon nucleophiles such as allylsilane, silylacetylenes, propargylsilane, and aromatic compounds in the presence of silver triflate to give the corresponding chain extended products at C-6 in high exo-selectivities. The product obtained from the reaction with propargylsilane was efficiently transformed into a naturally occurring heptopyranose derivative found in bacterial lipopolysaccharide.     

Electrochemically induced Favorsky rearrangement of alkyl benzyl ketones

Electrolysis of alkyl benzyl ketones in MeOH in an undivided electrolyzer in the presence of the NaI—NaOH mediator system induces the process similar to the Favorsky rearrangement to produce arylalkanecarboxylates in 80—90% yield (per substance) and with the 50—55% current efficiency.     

Photochemical reaction intermediates of benzyl chloride in condensed phase

Reaction intermediates produced upon the photolysis of benzyl chloride have been studied in glassy matrix and in solution. In the steady-state photolysis both benzyl radicals and structural isomers of benzyl chloride were formed in ethanol, while in 3-methylpentane the structural isomers were predominantly formed. The nanosecond laser photolyses of benzyl chloride in ethanol and in cyclohexane also generated benzyl radicals and structural isomers at room temperature. In acetonitrile, in addition to these species, benzyl cations were observed in the early stage after the photolysis.     

Photochemical reaction of benzaldehyde and benzyl alcohol with methyl acrylate

Conclusions The major low-molecular-weight product of the photochemical reaction of benzyl alcohol with methyl acrylate, in both the presence and absence of benzaldehyde, is the methyl ester of 4-methoxycarbonyl-6-oxo-6-phenylhexanoic acid (obtained in 2–16% preparative yield). The photolysis of systems containing a primary alcohol, the corresponding aldehyde, and methyl acrylate was found unsuitable for the preparation of 4-substituted-butanolides.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2384–2387, October, 1985.     

Kinetics and mechanism of the reaction of benzyl bromide with copper in hexamethylphosphoramide

The reaction of copper with benzyl bromides in hexamethylphosphoramide has been studied. The kinetic and thermodynamic parameters of the reaction have been obtained. Hammett plots of log (k/k^o) vs the substituent constant σ gave good correlations (ρ = 0.15, S_ρ = 0.02, r = 0.954). The structure of the organic group has little effect on the rate of reaction of benzyl bromide with copper. In the absence of atmospheric oxygen, the oxidative dissolution of copper occurred by the mechanism of single‐electron transfer with the formation of 1,2‐diphenylethane and copper(I) complexes. The stereochemistry and intermediates compound was also investigated. The reaction mechanism is discussed. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 296–305, 2005     

取代苄基瞵酸脂与取代苯甲醛反应的动力学研究

本文报导几种中等活性的瞵酸脂与各种取代苯甲醛反应的动力学研究, 并考查了中等活性的瞵酸脂组分及中等活性的醛组分上不同取代对反应速度的影响。     

Electrophilic aromatic addition reaction: electrophilic attack at an aromatic H substituent position

[reaction: see text] We report and propose a mechanism for an unusual electrophilic aromatic addition reaction (Ad(E)()Ar). During our preparation of 5,7-dibromo-8-methoxyquinaldine as a key intermediate in the synthesis of 7-bromoquinaldine-5,8-dione, direct bromination in either acidic or neutral conditions led only to the formation of 5-bromo-8-methoxyquinaldine. Under basic methanolic conditions, however, we unexpectedly obtained the 5,7-dibromo-8,8-dimethoxy-7,8-dihydroquinaldine adduct 2a. This result not only allows for the functionalization of aromatic compounds via the addition adducts, but also introduces the possibility of an alternate mechanism for electrophilic substitution reactions.     

Photodissociation dynamics of benzyl alcohol at 193 nm

Photodissociation dynamics of benzyl alcohol, C(6)H(5)CH(2)OH and C(6)H(5)CD(2)OH, in a molecular beam was investigated at 193 nm using multimass ion imaging techniques. Four dissociation channels were observed, including OH elimination and H(2)O elimination from the ground electronic state, H atom elimination (from OH functional group), and CH(2)OH elimination from the triplet state. The dissociation rate on the ground state was found to be 7.7 × 10(6) s(-1). Comparison to the potential energy surfaces from ab initio calculations, dissociation rate, and branching ratio from Rice-Ramsperger-Kassel-Marcus calculations were made.     

Kinetics and mechanism of benzyl chloride reaction with zinc in dimethylacetamide

Oxidative dissolution of zinc in the system of benzyl chloride-dimethylacetamide was investigated. The reaction stereochemistry as well as intermediates and reaction products formed were studied. The kinetic and thermodynamic parameters of the process were measured. The process was shown to follow the Langmuir-Hinshelwood mechanism with the formation of benzyl radicals and mono-solvated organozinc compound on the zinc surface. The components of mixture are adsorbed at various sites of the zinc surface, while recombination and the isomerization of the benzyl radicals occurs in solution.     

Kinetics and mechanism of nickel reaction with benzyl bromide in dimethylformamide

Abstarct  The reaction of nickel with benzyl bromide in DMF has been studied. The reaction intermediates were investigated by different methods and the kinetic and thermodynamic parameters were determined. The reaction of benzyl bromide with nickel was shown to occur on the metal surface by the Langmuir-Hinshelwood scheme, with the formation of benzyl radicals which are recombined and isomerized in solution to form 1,2-diphenylethane and trace amounts of 4.4′-dimethylbiphenyl. Original Russian Text ? A.M. Egorov, S.A. Matyukhova, I.S. Kocherova, A.A. Novikova, A.V. Anisimov, 2009, published in Zhurnal Obshchei Khimii, 2009, Vol. 79, No. 3, pp. 455–463.